1. Field of the Invention
The present invention relates to a device to time and actuate the extension and retraction of a racking platform for a well mast and, more particularly, to such a device which operates automatically upon the extension of the derrick.
2. Description of the Prior Art
On most well masts there is a platform which extends outward from an upper portion thereof and is used to hold or rack strings of drill tubing during the drilling operation or during well servicing. The racking platform may be fixed to the mast or may be pivotally connected for retraction while the rig and mast are moved. Certain forms of rigs are adapted to be attached directly to a large vehicle and are normally used to drill or service moderate depth wells. With these mobile rigs there is a need to keep the height, width and weight to certain maximum limits so that the mobile drilling rig may operate legally upon the roadway. So there is a need to retract the racking platform for movement of the rig and extend the platform at the time of set up.
The mast structure may be carried on the truck horizontally and either mechanically or hydraulically raised. These mast structures usually are segmented or telescoping with the upper portions telescoping upwards from a fixed lower structure. Various devices have been used to extend the racking platform in the past with mechanical or hydraulic power being used most often, however these forms of extension require separate power transmission or hydraulic lines to actuate the racking platform which increases weight, cost and maintenance requirements of the structure. Pulley cable systems have been used to extend and retract the racking platform which require a separate power source to actuate the platform provided by a separate motor or power take-off from the main electrical or hydraulic generator of the drilling rig.
Certain cable and pulley systems have been used which are actuated by the telescoping action of the mast sections. However these prior art systems have not provided flexibility in allowing for any length of mast and the extension of the platform could not be timed to extend after the telescoping action of the mast was sufficient to clear any obstacles, such as an oil well pumping unit.